In the October Global Futures Report, The Institute for Global Futures described neurowarfare as follows:
Shape shifting realities, contextual synthetic intelligence, mind morphing...if none of this sounds familiar, that's okay as NeuroWar has not been invented ---maybe. NeuroWar, the use of advanced neuroscience technology for defense is in it's embryonic stages.

Neuroweapons might be on the horizon, but being close to government-funded/military research, it seems to me that field-operable weapons are likely many decades off.

One sample roadblock to consider: distribution. Aerosol-based brain agents would likely be deemed chemical weapons which are internationally outlawed.

And while my knowledge of phrama & respiratory physiology is limited to that of a pre-med level, it seems to me that another one of the major issues with such drug-based neuroweapons would be ensuring proper dosage-levels. Examples of uncontrolled aerosol-based 'control' devices used in realistic settings have proven to be very unpredictable--- as was evidenced in the Russian siege of Muslim/Chechnyan-held Moscow theatre where seemingly understood dosage-levels of a believed opiate-(fentanyl-based?)oriented gas did not have the desired incapacitating effect (it killed many and left many others unaffected).

As an aside, I came across another magnetic-based (TMS) brain device/research project that is intended to improve soldier performance that is hardly high-tech, but certainly interesting:

http://www.musc.edu/pr/darpa.htm

Anyway, those people interested in the on-goings of defense-based research can check out DARPA's life of unclassified programs (pdf):

http://www.darpa.mil/body/pdf/FINAL2003FactFilerev1.pdf

If you are a fan of induction: keep in mind that it was DARPA (and not Al Gore) that brought us the internet, so the forces of DARPA certainly aren't always as sinister as many people would like to believe....

I'm a systems-level neuroscience guy anyway, so receptor-side pharma-physiology really tends to inhibit my brainstem :) I'd still place a wager that controlling dosage across multiple orders of magnitude for both the chemical weapon dujour and the receptor-specific agonist is just one, of many, potential problems to chemical-based neuroweopons.

Would a 30-40 fold increase in the dosage of fentanyl + the Manke et al 5-HT4 receptor-specific agonist still be fatal?

I dont really want to belabor this point since I only brought up Moscow as a popularized example of primitive neurowar gone bad(ly). But by extension, if simply trying to knock-out some terrorists in a closed environment went this badly (and there's lots of reasons to believe that things turned out "best-case"), trying to have widespread, profound effects on higher-level cognition, especially in the context of the current military doctrine, seems like quite an intractable problem at the moment. I certainly wouldnt want to send my kid into secure a hostile area (or pacify friendly noncombatants, for that matter) where random doses of psychotropics were used